MAYBE

We are left with following problem, upon which TcT provides the
certificate MAYBE.

Strict Trs:
  { is_empty(nil()) -> true()
  , is_empty(cons(x, l)) -> false()
  , hd(cons(x, l)) -> x
  , tl(cons(x, l)) -> cons(x, l)
  , append(l1, l2) -> ifappend(l1, l2, is_empty(l1))
  , ifappend(l1, l2, true()) -> l2
  , ifappend(l1, l2, false()) -> cons(hd(l1), append(tl(l1), l2)) }
Obligation:
  innermost runtime complexity
Answer:
  MAYBE

The input cannot be shown compatible

Arrrr..